Rock Collection Science

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Introduction

Sonja Radmilovic Rock Collection Science 9-1 27/4/02 Rocks are composed primarily of minerals and can be an amalgam of different minerals or can be composed of one mineral. Over 3500 minerals have been identified; most of these can be found in the earth's crust. Some of the earth's minerals are exceedingly popular - fewer than 20 minerals compose more than 95% of the earth's crust. There are three different ways rock can be created on earth and thus there are three main classifications of rock, based on the three processes - igneous, sedimentary, and metamorphic. The rock cycle represents the alteration of rock-forming minerals above and below the earth's surface. At the top of the diagram molten rock material, magma, cools (crystallization) to form igneous rocks. If magma is extruded on to the surface it is called lava. Cooling above the surface yields rocks with fine textures, while those that form from slow cooling beneath the surface typically have large crystals. Igneous rock may melt when exposed intense heat to form magma again, or be changed into metamorphic rock. Igneous rocks may also be exposed to weathering, erosion and deposition to form sediment, the precursor for sedimentary rock. As sediments accumulate they are subjected to compaction and cementation to form sedimentary rock. Sedimentary rock usually displays layers or strata representing episodes of sediment deposition. Sedimentary rocks may be broken down again by weathering and erosion to be deposited as sediment, exposed to intense heat and melting to return to magma, or be changed into a metamorphic rock. Metamorphic rocks are those that have been altered to due exposure to heat or pressure. The pressure can be created by the weight of material lying above them. The grinding of lithospheric plates can create pressure and heat that will alter rock as well. If entirely melted, the rock material forms magma. Erosion and weathering can break down metamorphic rocks to form sediment, which can be compacted into sedimentary rock. ...read more.

Middle

Chalk crayons for artistic drawing usually have been confined to the colors white (limestone), black (soft black stone or a composition including lampblack), and red (natural pigments). The colored chalk crayons used in schools for writing or drawing on chalkboards are composed of powdered pigments mixed with powdered white chalk and a non-greasy binder. A drawing material much like the chalk crayon is the pastel, which consists of any of a variety of pigments in a synthetic binder such as methyl cellulose. After gathering this information I decided to do an old experiment, which is still used for testing to see if the rock is chalk. As you might already know chalk fizzes when acid is dropped on it. This happens because chalk is made of calcium carbonate. So what I did was take the rock I found and carefully with a small plastic needle I poured a few drops of acid over the rock. And it started to fizz. This is how I came to the conclusion that the rock, which I found was chalk. Limestone- Well when I heard we had to do a rock-collecting project I knew just where to find a limestone. We have a community gardens in our neighborhood and they use limestone and marble to put around plants as decoration. So I went down to the garden and took one of the limestone's. When I came home I decided to do some research on it. Here is what I learned: Without help from chemistry and a microscope it would be hard to accept that the rock called limestone comes from sea shells and corals. But chemistry proves that shells and corals owe their stiffness to calcium carbonate (CaCO3), often called "carbonate of lime." Limestone also is mainly calcium carbonate; and the microscope reveals the remains of animals that formed it. Limestone is sedimentary rock, formed from shells and other "limey" material in the oceans that in past ages covered the limestone regions. ...read more.

Conclusion

The principal minerals in slate are mica, chlorite, and quartz. Slate was used in earlier times to make flat writing tablets called slates, tombstones, roofing tiles, and other articles that required a smooth, flat surface. Later this dark gray (sometimes blue, greenish, purplish, or even red) stone came into wide use in such items as roofing, sinks, washtubs, flooring, blackboards, billiard tabletops, and mantels. Slate is especially suitable for these uses because of its smooth, easily cleaned surface and its property of splitting into thin slabs or leaves. The different colors of slate are due to the presence of various minerals in the rock. Shale is formed from fine-grained sediments deposited in quiet, protected waters such as the deep ocean floor, the deeper parts of continental shelves, shallow seas and bays, coastal lagoons, and river floodplains. Most shales are composed of clay minerals, quartz, and such other substances as carbonates, feldspars, iron oxides, and organic matter arranged in thin layers. Colors in shale are caused by the presence of certain minerals and organic substances. Black shale, for example, results from organic matter, red shale from ferric iron, and green shale from ferrous iron. Shale is soft and porous, characteristics that allow it to absorb and release organic matter and minerals easily. Trapped organic material may be converted into petroleum and other hydrocarbons. Shale has considerable economic value. Oil is extracted from shale in the United States, Brazil, and South Africa. Petroleum from this source, however, cannot be refined by methods used for crude oil. To render shale oil usable, hydrogen must be added and the mixture treated chemically to remove nitrogen and impurities. Shale in the eastern United States is a rich source of uranium. A large band of this sedimentary rock in Central Europe contains metallic sulfides, and shale deposits in eastern Germany and Poland are mined for their copper, lead, and zinc. The reasons I believe this rock is a slate rock are because it is a blackish golden color, it's a hard rock but it splits into sheets easily. Just like a slate rock is. ...read more.

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